Add usage stats to quotas page

What does this MR do?

Changes are behind additional_repo_storage_by_namespace feature flag (yml file)

In this iteration:

Adds the following statistics in the group/profile Usage Quotas page. The BE for this is not ready yet but the FE (in this MR) adds skeletons with fake data.

• Total namespace storage used
• Total excess storage used
• Purchased storage available

Note: The links in the boxes are not accurate as the documentation MRs are not in yet.

Previous iterations:

• Update the Quotas Page table !43080 (merged)
• Introduce error state and remove collapsible section !43644 (merged)
• Introduce warning state and tooltips for Quotas Page table: !44396 (merged)

Demo

https://gitlab-review-usage-quot-6vkjxd.gitlab-review.app/groups/gitlab-qa-sandbox-group/-/usage_quotas#storage-quota-tab

Screenshots

Designs are here

Before	After
Without feature flag enabled --->

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Mentions: https://gitlab.com/gitlab-org/gitlab/-/issues/247831